Larval Stages Of Fish Research Articles

Assessing Environmental Control on Temporal and Spatial Patterns of Larval Fish Assemblages in a Marine Protected Area

The northern coast of the Iberian Peninsula is an important spawning and nursery area for several marine fish species, some of which are economically exploited by fisheries and under management plans. Larval stages of fish are highly sensitive to environmental change and anthropogenic pressures, and Marine Protected Areas (MPA) can help mitigate the impacts on fish populations. This study investigated the environmental drivers of the temporal and spatial patterns of the larval fish assemblages inhabiting a small coastal MPA along the NW Portuguese Iberian Coast. Seasonal surveys were conducted over two years at nine sampling stations distributed throughout the MPA to collect larval fish samples and water parameters. Results showed that a total of 39 different fish taxa were identified. In terms of abundance, reef-associated species, such as Parablennius gattorugine (54.6%), and marine species that use estuaries as nursery areas, such as Ammodytes tobianus (15.7%) and Clupeidae n.i. (8.8%) dominated the larval fish assemblages. The larval fish assemblages were characterized by a strong temporal pattern that, according to CCA analyses, was related to the temporal variability of water temperature, pH, chlorophyll α, TPM, and also the river flow of an adjacent river. This study showed that 47% of the fish larvae belonged to commercially exploited species, highlighting the importance of this MPA as a nursery area for the early life stages of the fish population. Overall, these new findings emphasize the role of MPAs in ensuring the connectivity of fish species between marine-estuarine habitats and enhancing the conservation of fish populations.

Environmental influences, particularly river flow alteration, on larval fish assemblages in the Douro Estuary, Portugal

Larval stages of fishes are highly vulnerable to environmental shifts and anthropogenic pressures can pose additional stress to such a critical phase. The present study aimed to investigate environmental controls on the larval fish assemblages of the Douro Estuary, a heavily modified water body with several anthropogenic pressures. Monthly sampling surveys were conducted over two years along the estuarine horizontal gradient. The estuarine larval fish assemblage was dominated by a few very abundant taxa. Resident Pomatoschistus microps and members of the marine Clupeidae and Soleidae families were the most abundant taxa, accounting for 87.5% of the total catch. Canonical correspondence analysis identified e.g., river flow and salinity as the main environmental variables regulating the larval fish assemblages in the Douro Estuary. River flow had a significant impact on larval fish abundances with the lowest abundances observed when river flow surpassed 900 m3 s−1. Overall, the Douro larval fish assemblage exhibited similar features to other less impacted temperate estuaries. However, the results of this study highlighted the negative impact of regulating river flows that can compromise the connectivity of estuaries with adjacent coastal areas and, ultimately, their nursery function for the early life stages of fishes.

Sensory-Motor Perturbations in Larval Zebrafish (Danio rerio) Induced by Exposure to Low Levels of Neuroactive Micropollutants during Development.

Due to increasing numbers of anthropogenic chemicals with unknown neurotoxic properties, there is an increasing need for a paradigm shift toward rapid and higher throughput behavioral bioassays. In this work, we demonstrate application of a purpose-built high throughput multidimensional behavioral test battery on larval stages of Danio rerio (zebrafish) at 5 days post fertilization (dpf). The automated battery comprised of the established spontaneous swimming (SS), simulated predator response (SPR), larval photomotor response (LPR) assays as well as a new thermotaxis (TX) assay. We applied the novel system to characterize environmentally relevant concentrations of emerging pharmaceutical micropollutants including anticonvulsants (gabapentin: 400 ng/L; carbamazepine: 3000 ng/L), inflammatory drugs (ibuprofen: 9800 ng/L), and antidepressants (fluoxetine: 300 ng/L; venlafaxine: 2200 ng/L). The successful integration of the thermal preference assay into a multidimensional behavioral test battery provided means to reveal ibuprofen-induced perturbations of thermal preference behaviors upon exposure during embryogenesis. Moreover, we discovered that photomotor responses in larval stages of fish are also altered by the as yet understudied anticonvulsant gabapentin. Collectively our results demonstrate the utility of high-throughput multidimensional behavioral ecotoxicity test batteries in prioritizing emerging risks associated with neuroactive drugs that can perturb neurodevelopment. Moreover, we showcase the added value of thermotaxis bioassays for preliminary screening of emerging contaminants.

Immunotoxicity responses to polystyrene nanoplastics and their related mechanisms in the liver of zebrafish (Danio rerio) larvae.

Nanoplastics in aquatic environments may induce adverse immunotoxicity effects in fish. However, there is insufficient evidence on the visible immunotoxicity endpoints in the larval stages of fish. The liver plays an important role in systemic and local innate immunity in the fish. In this study, the hepatic inflammatory effects of polystyrene (PS) nanoplastic particles (NPs: 100 and 50nm) and micron PS particles on transgenic zebrafish (Danio rerio) larvae were estimated using fluorescent-labeled neutrophils, macrophages, and liver-type inflammatory binding protein (fabp10a). Particles with smaller size induced higher aggregations of neutrophils and apoptosis of macrophages in the abdomen of the larvae, corresponding to greater hepatic inflammation in the larvae. NPs increased the expression of fabp10a in the larval livers in a dose- and size-dependent manner. PS particles of 50nm at a concentration of 0.1mg·L-1 increased the expression of fabp10a in the larval liver by 21.90% (P<0.05). The plausible mechanisms of these effects depend on their distribution and the generation of reactive oxygen species in the larvae. Metabonomic analysis revealed that the metabolic pathways of catabolic processes, amino acids, and purines were highly promoted by NPs, compared to micron PS particles. NPs also activate steroid hormone biosynthesis in zebrafish larvae, which may lead to the occurrence of immune-related diseases. For the first time, the liver was identified as the target organ for the immunotoxicity effects of NPs in the larval stage of fish.

Oceanographic influences on the early life stages of a mesopelagic fish across the Chilean Patagonia

Environmental conditions, such as sea surface temperatures and salinities, may exert important influences on the life history traits of marine organisms, particularly on the early stages of fishes. We studied the interaction between spring environmental conditions, egg and larval abundances, and growth rates, of pearlside Maurolicus australis along a 10° latitudinal range in western Patagonia. Using onboard field experiments, otolith-based back-calculated daily growth rates, CTD data, together with sea surface temperature (SST, 2002–2019) and chlorophyll-a (Chl-a, 2017–2018) satellite images, we studied the effect of short-term mesoscale variability on larval growth as well as their interactions with environmental conditions. SST of 2017 and 2018 were similar, with colder than average (2003–2018) springs for both years. Onboard experiments indicated that egg size directly influenced the size-at-hatch, though this was independent of lipid reserves. Larvae were categorized into Oceanic (Oc), Inner Seas (IS) and off the Southern Ice Fields (SIF). On the shelf (Oc), larvae were more abundant with faster growth rates; a second maximum density was observed off the SIF. The latter individuals had the smallest otolith-at-size and showed the slowest recent growth rates, despite spatially coinciding with relatively large Chl-a concentrations (>8 mg m−2). Latitudinally, the decrease in sea surface temperatures and the rise in vertical salinity gradients, reduced the recent larval growth of the pearlside. However, daily fluctuations in SST did not trigger significant variations in the back-calculated detrend growth rates. Although low temperatures in the SIF lead to slow growth rates of M. australis, compared to the northern population, the area presents some benefits regarding food availability, retention and protection from predators. Moreover, it is possible that the low temperatures might affect the energy balance of fish larval stages by intervening in the allocation of energy for tissue formation and metabolism, resulting in slow growth rates in the southern population.

Does weighting presence records improve the performance of species distribution models? A test using fish larval stages in the Yangtze Estuary

To obtain realistic forecasts of the impacts of climate change on species habitat suitability, novel approaches based on species distribution models (SDMs) are being developed and scrutinized. We argue here that, when dealing with data from long-term monitoring programmes, incorporating a temporal weight on the occurrence points may result in a more realistic prediction of a species' potential distribution. Using larval fish presence records collected from 1999 to 2013 in the Yangtze Estuary, China, we compared the performance of ensembles of standard SDMs versus SDMs constructed with weighted time-series presence records in predicting the present and future distributions of the larval stages of two dominant fish. The results of the ensemble SDMs showed that weighted presence records can significantly improve SDM performance, as measured through standard validation metrics. The SDM projections suggest that suitable habitat for both species will decrease under future climate scenarios, with one species (Stolephorus commersonnii) predicted to be more susceptible to climate change than the other (Engraulis japonicus). In addition to range contraction, model projections suggest that the future habitats of both species will shift northward—an implication of climate change that should be considered in future management and conservation strategies for the Yangtze Estuary.

Modelling the potential impacts of climate change on the distribution of ichthyoplankton in the Yangtze Estuary, China

AbstractAimSpecies distribution models (SDMs) are an effective tool to explore the potential distribution of terrestrial, freshwater and marine organisms; however, SDMs have been seldom used to model ichthyoplankton distributions, and thus, our understanding of how larval stages of fishes will respond to climate change is still limited. Here, we developed SDMs to explore potential impacts of climate change on habitat suitability of ichthyoplankton.LocationYangtze Estuary, China.MethodsUsing long‐term ichthyoplankton survey data and a large set of marine predictor variables, we developed ensemble SDMs for five abundant ichthyoplankton species in the Yangtze Estuary (Coilia mystus, Hypoatherina valenciennei, Larimichthys polyactis, Salanx ariakensis and Chelidonichthys spinosus). Then, we projected their habitat suitability under present and future climate conditions.ResultsThe ensemble SDMs had good predictive performance and were successful in estimating the known distributions of the five species. Model projections highlighted two contrasting patterns of response to future climates: while C. mystus will likely expand its range, the ranges of the other four species will likely contract and shift northward.Main conclusionsAccording to our SDM projections, the five ichthyoplankton species that we tested in the Yangtze Estuary are likely to respond differently to future climate changes. These projected different responses seemingly reflect the differential functional attributes and life‐history strategies of these species. To the extent that climate change emerges as a critical driver of the future distribution of these species, our findings provide an important roadmap for designing future conservation strategies for ichthyoplankton in this region.

DNA barcoding and morphological taxonomy: identification of lanternfish (Myctophidae) larvae in the Gulf of Mexico

Accurate identification of fish larval stages is complicated and time-consuming due to the lack of diagnostic morphological characters, especially during early developmental stages. The distribution of lanternfish (Myctophidae) has been described based on the morphological identification of adult stages. Larvae of only a few species of Myctophidae have been described, and the description is not always precise. In this study, larvae were collected and morphologically identified as Diaphus mollis, Hygophum hygomii, H. reinhardtii, H. taaningi, Myctophum obtusirostre and M. selenops. The DNA barcode region of the mitochondrial cytochrome oxidase I gene (COI) was determined for all larvae. The COI sequences matched reference barcodes available in GenBank for 14 of the identified larvae. The remaining COI sequences matched reference barcodes for different species of Myctophidae including Centrobranchus nigroocellatus, Diogenichthys atlanticus and Lepidophanes guentheri. This effort demonstrated the importance of integrated morphological and molecular analysis of species diversity and distribution of the Myctophidae in the Gulf of México.

Diatomix: A Diatoms Enhancer

Diatoms are unicellular aquatic microorganisms that belong to a major group of algae called the goldenbrown algae. Diatoms get energy from sunlight and grow use organic matter as food (Carbon source) grown in aquaculture pond. They are the major oxygen producers in the world generates 20% oxygen on the planet earth. Different species of diatoms are cultured/grown in marine water and freshwater which helps for the juveniles as their primary food for shrimp and fish fry. In the larval stages of fish fry/shrimp larvae diatoms are the first food of choice. A unique product Diatomix which enhances the growth of diatoms in the pond by its micro mineral nutrient composition helps full fill the nutritional needs of aquatic species.

The ‘suitcase hypothesis’: Can entrainment of meroplankton by eddies provide a pathway for gene flow between Madagascar and KwaZulu-Natal, South Africa?

Similarities in the marine fauna found off the coasts of southern Madagascar and KwaZulu-Natal Province (KZN), South Africa, led to the development of the ‘suitcase project,’ with the aim of establishing whether eddies that form off southern Madagascar may package and transport biological material across the Mozambique Channel, facilitating connectivity and gene flow. Meroplankton (larval stages of fishes and benthic invertebrates) were collected on the Madagascan shelf and along a transect through a cyclonic eddy in the Mozambique Channel. The samples were analysed using microscopy and DNA barcoding, seeking to identify species known to be common to both the southeast coast of Madagascar and the east coast of South Africa and thereby to reveal potential indicators of connectivity between these regions. The greatest zooplankton biovolume in the upper 200 m occurred on the shelf, followed by in the western part of the eddy and in the region outside the eddy to the west, and was lowest in the region outside the eddy to the east. The meroplankton were dominated by taxa of coastal origin and these were also most abundant on the shelf and in the western part of the eddy, with the lowest abundances in the region outside the eddy to the east. The findings show greater zooplankton biovolumes and larval abundances and the presence of reef-associated larval assemblages on the Madagascan shelf and along the transect through the cyclonic eddy, providing support for the suitcase hypothesis that planktonic organisms are entrained within eddies as they propagate south-westwards of the Madagascan shelf.

Trans-intestinal absorption rates differ between free amino acids during larval development in Atlantic herring (Clupea harengus)

Trans-intestinal absorption (TIA) rates for the free amino acids (FAA) alanine, proline, and glutamic acid were measured in two developmental phases of Atlantic herring larvae: Early (14–16day-post-hatch) and Late (37–39day-post-hatch). TIA rates were determined by measuring net uptake of a 14C-radiolabeled FAA tracer solution into the body after administration of a single bolus to the digestive tract by tube-feeding. Tracer solutions (concentration range: 0.02 to 100mM) were administered at <50% of gut volume (GV) and the response of TIA rate to increasing administered dose (pmol FAA ind−1) determined. GV was determined as the maximum volume of a tube-fed liquid bolus that could be retained in the digestive tract of a fasted larva without causing any evacuation from the mouth or anus, and was dependent on larval standard length. Our data revealed that alanine, proline and glutamic acid have different TIA rates (pmolmin−1), and results were consistent at both larval stages. At the same administered dose (pmol ind−1), the TIA rate for glutamic acid was only 8–25% of that of alanine and 15–30% of proline in both larval stages. In Early and Late larvae, the dose-dependent increase in proline and glutamic acid uptake was significantly more rapid than for alanine. Hence, alanine was the most rapidly absorbed FAA at low dose, followed by proline and then glutamic acid, but proline became more rapidly absorbed than alanine at the highest doses, in both stages. In conclusion, the study demonstrated that FAA representing neutral, imino and acidic classes, have different rates of absorption. Across a broad range of concentrations, Atlantic herring larvae have a much lower capacity to deliver glutamic acid from the intestinal lumen to body tissues relative to alanine and proline. Statement of relevanceThis paper provides important and quantitative information to understand uptake of different classes of dietary free amino acids in larval stages of fish. We use herring as model since it gives the best combination of size, transparency, robustness, gut morphology for in vivo tube feeding. The data is relevant for formulation of starter diets.

Effects of ocean acidification on the swimming ability, development and biochemical responses of sand smelt larvae

Ocean acidification, recognized as a major threat to marine ecosystems, has developed into one of the fastest growing fields of research in marine sciences. Several studies on fish larval stages point to abnormal behaviours, malformations and increased mortality rates as a result of exposure to increased levels of CO2. However, other studies fail to recognize any consequence, suggesting species-specific sensitivity to increased levels of CO2, highlighting the need of further research. In this study we investigated the effects of exposure to elevated pCO2 on behaviour, development, oxidative stress and energy metabolism of sand smelt larvae, Atherina presbyter. Larvae were caught at Arrábida Marine Park (Portugal) and exposed to different pCO2 levels (control: ~600μatm, pH=8.03; medium: ~1000μatm, pH=7.85; high: ~1800μatm, pH=7.64) up to 15days, after which critical swimming speed (Ucrit), morphometric traits and biochemical biomarkers were determined. Measured biomarkers were related with: 1) oxidative stress — superoxide dismutase and catalase enzyme activities, levels of lipid peroxidation and DNA damage, and levels of superoxide anion production; 2) energy metabolism — total carbohydrate levels, electron transport system activity, lactate dehydrogenase and isocitrate dehydrogenase enzyme activities. Swimming speed was not affected by treatment, but exposure to increasing levels of pCO2 leads to higher energetic costs and morphometric changes, with larger larvae in high pCO2 treatment and smaller larvae in medium pCO2 treatment. The efficient antioxidant response capacity and increase in energetic metabolism only registered at the medium pCO2 treatment may indicate that at higher pCO2 levels the capacity of larvae to restore their internal balance can be impaired. Our findings illustrate the need of using multiple approaches to explore the consequences of future pCO2 levels on organisms.

Effects of high water discharge from Alcalá dam on fish larval stages of Guadalquivir estuary

Event Abstract Back to Event Effects of high water discharge from Alcalá dam on fish larval stages of Guadalquivir estuary Juan Miguel Miró1*, César Megina1, Iñigo Donázar-Aramendía1, Emilio Sánchez-Moyano1, Isabel García-Asencio1 and J. Carlos García-Gómez1 1 Facultad de Biología, Universidad de Sevilla, Departamento de Zoología, Spain Estuaries are unstable systems, generally with a limited number of species. However, they support a high productivity, frequently being important nursery zones where postlarvae and juvenile fishes find some good conditions for its development. Most of estuaries have the freshwater input regulated by dams, altering estuarine natural hydrological regime. Nevertheless, high discharges can modify sharply column water structure, influencing organisms that live inside by eliminating salinity gradient or increasing turbidity and flow velocity. These changes affect nursery function of estuaries. In this study, we analyse the effects of freshwater input episode, which come from Alcalá Dam after a high rainfall, on larval stages of Guadalquivir estuary (Southwestern Spain). Sampling were carried out before (24 m3/s), during (151 m3/s) and after (14 m3/s) a high dam discharge. Samples were taken with a zooplankton net with 1 meter mouth diameter and 1000 µm mesh size. Double oblique tows were performed from surface to bottom during flood tide, in the main channel. Samples were taken along the estuarine section where larval stages had been detected, including some external marine areas (~35‰). In every sampling area 3-5 replicated tows were done. Physiochemical data of the water column were also recorded in all water masses with a multi-parameter probe (salinity, temperature, turbidity, HDO, depth and pH). First preliminary results were analysed. Data from probe showed relevant changes in water column parameters and, even if this is a well-mixed estuary, we observed a salinity stratification up until 15 grades from the bottom to the surface during high discharge episode. Abundance of fish juvenile phases decreased markedly during high fresh water inputs episode, although it recovered partially after a short period. Still, this effect was not equal for all species. Additional episodes of high dam discharge will be sampled and analysed to obtain a more general pattern and to propose management strategies related to river discharges. Acknowledgements We thank to Autoridad Portuaria de Sevilla (APS) for financial support. This work was partially supported by the V Plan Propio Universidad de Sevilla via a pre-doctoral grant. Keywords: Fish larval stages, Dam discharge, Water column structure, Nursery area, Guadalquivir estuary Conference: XIX Iberian Symposium on Marine Biology Studies, Porto, Portugal, 5 Sep - 9 Sep, 2016. Presentation Type: Poster Presentation Topic: 1. ECOLOGY, BIODIVERSITY AND VULNERABLE ECOSYSTEMS Citation: Miró J, Megina C, Donázar-Aramendía I, Sánchez-Moyano E, García-Asencio I and García-Gómez J (2016). Effects of high water discharge from Alcalá dam on fish larval stages of Guadalquivir estuary. Front. Mar. Sci. Conference Abstract: XIX Iberian Symposium on Marine Biology Studies. doi: 10.3389/conf.FMARS.2016.05.00118 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 29 Apr 2016; Published Online: 03 Sep 2016. * Correspondence: PhD. Juan Miguel Miró, Facultad de Biología, Universidad de Sevilla, Departamento de Zoología, Sevilla, Sevilla, 41012, Spain, jmmiro@us.es Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Juan Miguel Miró César Megina Iñigo Donázar-Aramendía Emilio Sánchez-Moyano Isabel García-Asencio J. Carlos García-Gómez Google Juan Miguel Miró César Megina Iñigo Donázar-Aramendía Emilio Sánchez-Moyano Isabel García-Asencio J. Carlos García-Gómez Google Scholar Juan Miguel Miró César Megina Iñigo Donázar-Aramendía Emilio Sánchez-Moyano Isabel García-Asencio J. Carlos García-Gómez PubMed Juan Miguel Miró César Megina Iñigo Donázar-Aramendía Emilio Sánchez-Moyano Isabel García-Asencio J. Carlos García-Gómez Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Seasonal changes on microbial metabolism and biomass in the euphotic layer of Sicilian Channel

As a part of a wider project on fisheries ecology, several biological and environmental parameters were monitored during two oceanographic cruises (BANSIC 2012 and NOVESAR 2013) in the Sicily Channel, which connects the Western and Eastern Mediterranean basins.The prokaryotic abundances and biomass as well as hydrolysis rates on organic matter were investigated in the euphotic layer of a retention area for fish larval stages including anchovy (Engraulis encrasicolus, Linnaeus, 1758) with the aim to investigate the different biogeochemical signatures in two seasonal conditions. The environmental parameters, particulate organic carbon and nitrogen together with heterotrophic production were also measured.Results showed significant increases for most of the studied parameters with increasing temperature during summer. This had effects on the Carbon cycle and recycling of nutrients; in fact total prokaryotic abundance and biomass, as well as carbon hydrolyzed by two enzymes (Leucine aminopeptidase and β-glucosidase), increased significantly during summer. Conversely Alkaline phosphatase activity, Chlorophyll concentration and Oxygen increased during winter. The same environmental parameters affected also the presence of fish eggs. Moreover high percentages of free enzymes (i.e., enzymes not associated with cells) were measured, accounting for percentages variable from 12 to 95 % of the total enzymatic activity, with values generally higher in summer than in winter.In this oligotrophic environment, the prokaryotic biomass was supported by the C hydrolyzed by enzymatic activities. The ratio between the hydrolyzed C and prokaryotic biomass was higher in winter than in summer, indicating that alkaline phosphatase activity contribute to an efficient incorporation of C into biomass in winter.

Do fish larvae have advantages over adults and other components for assessing estuarine ecological quality?

Using a novel approach to the assessment of ecological quality status of estuarine ecosystems, this study hypothesizes that compared to adult fishes and other components, the younger fish stages will be more sensitive and act as an early warning and will reflect more effectively the ecological status of estuaries. Larval stages of fishes were used to assess the ecological quality status (EQS) of four NW Portuguese estuaries, with different types and magnitudes of human pressures. The larval fish assemblages, together with water column characteristics and pollution indicators (faecal contamination and nutrient load) were sampled in the Lima, Cávado, Ave and Douro estuaries, during spring and autumn 2009. The four estuaries were classified in terms of human pressures by a global pressure index that identified the Cávado estuary as the least impacted estuary, followed by the Ave and Lima, both classified as moderately impacted system, while the Douro was classified as a highly impacted system. The Ave emerged as the most polluted system, carrying the highest nutrient load and sewage contamination. Larval fish assemblages included estuarine species, marine migrants, marine stragglers and the larger estuaries had higher species richness. Compared to adult fishes, three multimetric fish-based indices classified the Cávado, Ave and Douro estuaries with a lower ecological status when fish larvae were used. Similarly, the EQS assessed by macroinvertebrates were equal or higher when compared with fish larvae results. The EQS assessed by fish larvae was negatively correlated with sewage contamination and nitrogen nutrients, but did not reflect other anthropogenic pressures expressed by the global pressure index, which was only detected by adult fish. Fish larvae assessments were able to detect short-time events of hydrological manipulations observed in the Cávado estuary, as well as a seasonal decrease of water quality especially evident in the Ave estuary. The indices used denoted some limitations to the use of fish larvae data, thus emphasising the need for new indices to test the observed tendency for lower EQS given by fish larvae. The advantages and disadvantages of using fish larvae as more sensitive and accurate bioindicators of ecosystem integrity is also discussed as a means of providing strategically important information for improved estuarine management.

Microbiota of Salt Lakes as Food for the Brine Shrimp Artemia

The brine shrimp Artemia is often abundantly found in hypersaline environments.The larvae(‘nauplii’)hatching from its dormant embryos(‘cysts’)are a crucial live food item for the larval stages of fish and shrimp in aquaculture

Diet and prey selection in late-stage larvae of five species of fish in a temperate estuarine nursery

The plankton assemblage of the permanently open Sundays Estuary in South Africa was sampled seasonally to provide further information on the feeding ecology of the larval stages of fishes in temperate estuaries. Collections were made between winter 2007 and autumn 2009 at eight sites by means of boat-based plankton tows. Physico-chemical variability in the water column was typical for temperate systems. Mean density of larval fishes and zooplankton showed similar seasonal and spatial trends. Gut content analyses were conducted in five dominant larval fish species: Gilchristella aestuaria (Clupeidae), Pomadasys commersonnii (Haemulidae), Monodactylis falciformis (Monodactylidae), Myxus capensis (Mugilidae) and Rhabdosargus holubi (Sparidae). The first record of selective consumption of copepod eggs by G. aestuaria is reported. Insect larvae (chironimids) dominated the diet of some marine fish larvae (M. falciformis and M. capensis). The copepod Pseudodiaptomus hessei formed the largest volume of the diet of P. commersonnii whereas R. holubi selected for the amphipod Corophium triaenonyx, with P. hessei also being a frequently consumed prey item. Seasonal and spatial variability with salinity was evident in the diet. Larvae also showed changes in diet at different stages of development. Pelagic prey species constituted the largest volume of the diet of G. aestuaria whereas all other larvae consumed large volumes of bentho-pelagic prey. All larvae selected P. hessei as a prey item. Myxus capensis and R. holubi also selected this copepod and showed the largest diversity in diet.

Shallow-water, nearshore current dynamics in Algoa Bay, South Africa, with notes on the implications for larval fish dispersal

Nearshore currents play a vital role in the transport of eggs and larval stages of fish. However, little is known about their complexity and the implications for dispersal of fish larvae. The study describes the complexity of the shallow nearshore environment in eastern Algoa Bay, on the south-east coast of South Africa, and its effect on larval fish ecology. An ADCP was used to assess short-term spatial current variability across the nearshore (4–20 m depth) during intensive one-day-transect profiling surveys. Data showing long-term temporal variability was collected half-hourly from a bottom-moored (15–20 m depth) ADCP over the course of one year (May 2006–May 2007). The short-term profiling revealed complexity in both current speed and direction with largely wind-driven flow patterns identified. The long-term data showed that the currents were aligned approximately west/east with prevailing winds and local shoreline. Modal speeds of 8 cm s–1 near the surface (4 m) and 6 cm s–1 near the bottom (14 m) of the water column are much lower than the average swimming speeds of postflexion larvae known to occur in the area. Mean current speed decreased with depth from ∼30 cm s–1 (4 m) to ∼10 cm s–1 (14 m), suggesting opportunities for depth refuge from current displacement in older larvae. Potential nett displacements were greater during the spring and summer, coinciding with peak fish breeding with passive eggs and early stage larvae travelling distances of up to 475 km near the surface of the water column. These maximum dispersal distances recorded during the present study differ considerably by half that from other calculations made for the area, highlighting a data error in a previous study. These predictions provide preliminary indications of potential transport from a point source and do not factor in anomalous local oceanography, benthic topographic impediments to transport or the complexities of larval fish behaviour.

Feeding behaviour and digestive physiology in larval fish: current knowledge, and gaps and bottlenecks in research

AbstractFood uptake follows rules defined by feeding behaviour that determines the kind and quantity of food ingested by fish larvae as well as how live prey and food particles are detected, captured and ingested. Feeding success depends on the progressive development of anatomical characteristics and physiological functions and on the availability of suitable food items throughout larval development. The fish larval stages present eco‐morpho‐physiological features very different from adults and differ from one species to another. The organoleptic properties, dimensions, detectability, movements characteristics and buoyancy of food items are all crucial features that should be considered, but is often ignored, in feeding regimes. Ontogenetic changes in digestive function lead to limitations in the ability to process certain feedstuffs. There is still a lack of knowledge about the digestion and absorption of various nutrients and about the ontogeny of basic physiological mechanisms in fish larvae, including how they are affected by genetic, dietary and environmental factors. The neural and hormonal regulation of the digestive process and of appetite is critical for optimizing digestion. These processes are still poorly described in fish larvae and attempts to develop optimal feeding regimes are often still on a ‘trial and error’ basis. A holistic understanding of feeding ecology and digestive functions is important for designing diets for fish larvae and the adaptation of rearing conditions to meet requirements for the best presentation of prey and microdiets, and their optimal ingestion, digestion and absorption. More research that targets gaps in our knowledge should advance larval rearing.

Some biological characteristics of early larvae Dacodraco hunteri (Notothenioidei: Channichthyidae) in the western Ross Sea

Ichtyoplankton surveys were carried out in the western Ross Sea by the R/V Italica in the austral summer 1996 and 1997–1998 to study species composition and spatial distribution of larval stages of fish. One of the most abundant icefish caught was Dacodraco hunteri, a poorly known channichthyid inhabiting the high-Antarctic Zone. Based on 382 yolk-sac larvae and 13 preflexion larvae, the study was focused to estimate spatial distribution and abundance, as well as diet and growth rate. The pigmentation pattern and some morphometric measurements were also recorded for comparative purposes. The specimens were caught in relatively restricted areas located in Terra Nova Bay and north of the Ross Ice Shelf on the Challenger and Joides Basins. The standardized abundance of early larvae ranged between 0.03 and 1.72 individuals 10−3 m3 in 1996 and 0.16–4.53 individuals 10−3 m3 in 1997–1998, respectively. Fitting a linear model to the mean length increase in larvae collected in subsequent catch dates, the growth rate was estimated to be approximately 0.11 mm/day. Based on back calculation of growth rate and presumed hatch size of 11 mm, larval hatching probably took place in mid-December. Diet of preflexion larvae consisted exclusively of larvae of the pelagic nototheniid Pleuragramma antarcticum, a key species of the high-Antarctic pelagic food web. Hence, D. hunteri probably plays a more important role than previously thought in the pelagic community of the Ross Sea.